RE: How much RAM is to much
- From: "Taylor, Chris David" <ChrisDavid.Taylor@xxxxxxxxxxxxxxx>
- To: "'andrew.kerber@xxxxxxxxx'" <andrew.kerber@xxxxxxxxx>, 'Gaja Krishna Vaidyanatha' <gajav@xxxxxxxxx>
- Date: Thu, 10 Feb 2011 13:57:34 -0600
Doesn't direct IO have to configured in the mount options for the filesystems?
(Not just specified in the Oracle parameters)
Otherwise, you're in fact not using it, right?
Or do filesystems now-a-days get mounted with direct as an option automatically
in Linux?
Chris Taylor
Sr. Oracle DBA
Ingram Barge Company
Nashville, TN 37205
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From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Andrew Kerber
Sent: Thursday, February 10, 2011 1:54 PM
To: Gaja Krishna Vaidyanatha
Cc: RStorey@xxxxxxxxxxxxxxxxxx; oracle-l-freelists
Subject: Re: How much RAM is to much
That's a rather off the wall comment Everyone uses direct IO, its standard for
Oracle these days. I suppose some people may disable it if they are using a
file system (I rather doubt), but am not even sure you can configure ASM to not
use it. I cant imagine why anyone would try, for that matter.
On Thu, Feb 10, 2011 at 1:48 PM, Gaja Krishna Vaidyanatha
<gajav@xxxxxxxxx<mailto:gajav@xxxxxxxxx>> wrote:
Andrew et. al,
The percentage depends on whether or not direct I/O is configured and is
working per specification. If you have direct I/O properly configured, in the
big picture, the consumption of memory by the filesystem buffer cache will not
affect your memory consumption numbers. But if you do NOT have direct I/O
configured and depending on your operating system (Linux vs. Unix), the issue
then is what are the ceilings setup for the filesystem buffer cache's memory
consumption. The last time I checked there is no equivalent of "bufhwm"
(Solaris) or file_cache_max_pct (HP-UX) on Linux. Which means that if you don't
have direct I/O configured on Linux (which btw is not good practice), you can
be pretty much guaranteed that up to 100% of configured memory can be utilized
by the OS for the filesystem buffer cache. There have been many customer cases
in the past few years, where the lack of direct I/O has caused significant
paging/swapping overhead. The lack of direct I/O will also increase "sys" CPU
utilization and causing unnecessary overhead and contention on the system. Not
at all worth it!
Bottom line - please enable direct I/O, make sure it is working (by performing
the relevant truss, strace etc) and then finalize the memory allocations for
your SGAs & PGAs.
Cheers,
Gaja
Gaja Krishna Vaidyanatha,
Founder/Principal, DBPerfMan LLC
http://www.dbperfman.com
Phone - 001-(650)-743-6060
Co-author:Oracle Insights:Tales of the Oak Table -
http://www.apress.com/book/bookDisplay.html?bID=314
Co-author:Oracle Performance Tuning 101 -
http://www.amazon.com/gp/reader/0072131454/ref=sib_dp_pt/102-6130796-4625766
________________________________
From: Andrew Kerber <andrew.kerber@xxxxxxxxx<mailto:andrew.kerber@xxxxxxxxx>>
To: RStorey@xxxxxxxxxxxxxxxxxx<mailto:RStorey@xxxxxxxxxxxxxxxxxx>
Cc: oracle-l-freelists <oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>>
Sent: Thu, February 10, 2011 11:18:28 AM
Subject: Re: How much RAM is to much
I generally use the rule of thumb for Linux/unix of oracle can have up to 80%
of the RAM on the system on a dedicated server. However, make sure everything
on the OS is configured per the installation instructions for oracle before you
start dedicating all those resources to oracle.
On Thu, Feb 10, 2011 at 1:02 PM, Storey, Robert (DCSO)
<RStorey@xxxxxxxxxxxxxxxxxx<mailto:RStorey@xxxxxxxxxxxxxxxxxx>> wrote:
So, I'm moving my 9i 32 bit database to a 10g 64 bit database. My 9i box has 4
gig of ram and the usual 23bit limitations. My SGA and such on the 9i box
probably hovers around 1.2gig.
I have 24 gig of ram on the new box. From a data aspect, that will darn near
load my entire database to memory.
So, in setting SGA_TARGET, how much is too much? Before I was told the box
specs, I was thinking 3 gig. But, with 24 gig available, and I'm the ONLY
application on the box....how much is to much?
What are the benefits and cons to setting this value at say, 12gig, with a
SGA_MAX value of 15G.
--
Andrew W. Kerber
'If at first you dont succeed, dont take up skydiving.'
--
Andrew W. Kerber
'If at first you dont succeed, dont take up skydiving.'
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